Gas turbine engines conventionally include a rotor shaft and several rows of rotor blades, each row including multiple blades distributed circumferentially about the rotor shaft. In between the rows of blades are rows of stationary vanes. Combustion gases flow along the gas turbine engine longitudinal axis in an annular flow path defined by the blades and vanes. The rotor shaft lies radially inward of the annular flow path and a rotor cavity is formed between the rotor disk and a stator structure holding the stationary vanes. Cooling air, or rotor purge air is often directed into the rotor cavity. The purge air cools components within the rotor cavity that support the blades and vanes, after which the purge air typically exits the rotor cavity through a gap between the vanes and the blades on a radially inward end of the vanes and blades.
Combustion gases traveling in the annular flow path tend to form a “bow wave” immediately upstream of any components the gases encounter, such as a blade or vane. As a result, pressure builds up within the combustion gases immediately upstream of each blade. The bow waves are distributed circumferentially about the gas turbine engine, just radially outward of the gap. In order to prevent ingestion of the combustion gases into the gap and the rotor cavity, flow discouraging seals are often formed just inside the gap, slightly upstream of an outlet of the gap.
Flow discouraging seals may be formed via an angel wing, which uses a platform that extends axially from a base of the blade, together with a radially raised lip extending radially outward from a tip of the axial platform, to form a restriction in the gap intended to limit the flow of purge air outward, and combustion gases inward. The radially raised tip is conventionally axially aligned with an opposing surface, such as a surface on the stationary vane, which forms the restriction that acts as the flow discouraging seal.
It is known that the purge air has an aerodynamic impact on the flow of combustion gases where they interface, and various approaches have been taken to mitigate the impact. For example, U.S. Pat. No. 8,083,475 to Bulgrin et al. discloses an angel wing compression seal that guides the rotor air traversing the angel wing to a region in front of the respective blade. However, this patent appears to be limited to addressing the bow wave. Addressing other aerodynamic impacts, as well as addressing aerodynamic impacts for different blade geometries, leaves room in the art for improvement.